Different types of acoustic devices have been used through the years. One type of device is a microphone. In a microelectromechanical system (MEMS) microphone, a MEMS device includes at least one diaphragm and at least one back plate. The MEMS device is supported by a substrate and enclosed by a housing (e.g., a cup or cover with walls). A port may extend through the substrate (for a bottom port device) or through the top of the housing (for a top port device). In any case, sound energy traverses through the port, moves the diaphragm and creates a changing potential of the back plate, which creates an electrical signal. Microphones are deployed in various types of devices such as personal computers or cellular phones.
Moisture, dust, and other particles may travel through the port opening and contact the MEMS device. Particles as small as a few microns can interfere with microphone performance, especially at high sound-pressure-levels.
Some ingress protection practices have been used to prevent particles from traversing through the port and contacting the MEMS device. For instance, porous membranes made from poly-tetra-fluoro-ethylene (PTFE) or ultrahigh-molecular-weight-polyethylene (UHMWPE) may be provided near a port. Such membranes have several drawbacks. For example, the manufacture and installation of such membranes add additional steps during assembly of the microphone. Furthermore, the acoustic characteristics of such membranes often cause undesirable noise or otherwise degrade device performance. Vibration of a membrane may also produce unwanted signals within the microphone. Additionally, the membrane microstructure may not be optimal for specific applications. These and other drawbacks have resulted in some user dissatisfaction with previous approaches.
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